Diesel Trouble Codes

P0207 — Injector Circuit/Open - Cylinder 7 — LB7 Duramax

The ECM has detected an electrical fault in the cylinder 7 injector circuit. On the LB7 the injectors sit under the valve covers and are a well-known weak…

Updated October 15, 2026

What it means

The ECM has detected an electrical fault in the cylinder 7 injector circuit.1

Most likely causes

  1. Injector harness or connector fault under the valve cover on cylinder 7 — The LB7 injector harness and connector under the valve cover can chafe, corrode, or lose terminal tension, producing an open or high-resistance path to the injector. Inspect the under-valve-cover harness and connector for damage, oil intrusion, and terminal condition.1
  2. Faulty cylinder 7 injector (electrical open or internal coil failure) — LB7 injectors are a known weak point and can develop internal electrical opens or cracked bodies that affect the injector circuit. Electrical testing of the injector coil and comparison to other cylinders helps isolate a failed injector.1
  3. ECM driver or wiring fault between ECM and valve cover — An open or high-resistance wire, poor ground, or ECM driver issue on the cylinder 7 injector control circuit can set the code. Verify continuity and isolation of the injector control wire from the ECM to the valve-cover pass-through.1

How to diagnose

  1. Verify the code is present and check for accompanying misfire or fuel-in-oil symptoms. Review freeze frame for conditions at set.
  2. Inspect the under-valve-cover injector harness and connector for cylinder 7 for chafing, oil contamination, corrosion, or loose terminals. Compare to adjacent cylinders.
  3. Perform electrical tests at the injector connector for cylinder 7 (coil resistance and circuit continuity to ECM) and compare values to other cylinders to identify an open or high resistance.
  4. If the harness and external wiring test normal, the injector itself is suspect; plan injector replacement with proper under-valve-cover service procedures and post-repair balance-rate verification.
  5. Clear codes, run the engine through a representative drive cycle, and confirm the code does not return. Monitor injector balance rates and rail pressure for normal operation.

Specs and test values

CheckNormal readingWhen to measureSource
Injector balance ratesHealthy engines sit near ±2 mm³; values near ±4 mm³ or one cylinder far from the rest need a closer lookHot idle in Park, A/C offBD Diesel

Common mistake to avoid

Buying injectors on balance rates alone. Compression, rail pressure and the pressure regulator all move balance rates; confirm a suspect injector with a return-flow test before replacing it. Source: BD Diesel — LB7 injectors: balance rates and return tests.

Parts and tools you may need

Tools you’ll need

Rough cost and difficulty

Likely repairPartsShop laborWho usually does it
Wiring or connector repair$10–$1001–4 hrsDIY with tools and a manual
Injector wiring harness / under-valve-cover harness$50–$3002–5 hrsShop
Fuel injector (each)$250–$4502–4 hrsShop

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If the injector tests good electrically but the code persists, or if multiple injector circuit codes appear, have the ECM driver circuit evaluated by a qualified diesel technician with scope testing before replacing additional parts.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources

  1. Curated DTC seed — LB7 Duramax (curated) ↩︎ ↩︎ ↩︎ ↩︎